﻿using System;
using System.Linq;
using System.Linq.Expressions;

namespace Hollysys.Mes.Common.ExtensionsMethods
{
    public static class QueryExtensions
    {
        /// <summary>
        /// Linq排序扩展方法
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="source"></param>
        /// <param name="propertyName">属性的字符串名称</param>
        /// <param name="sort">方向</param>
        /// <returns></returns>
        public static IQueryable<T> SortBy<T>(this IQueryable<T> source, string propertyName, SortDirectionEnum sort)
        {
            if (source == null)
            {
                throw new ArgumentNullException("source");
            }

            if (String.IsNullOrEmpty(propertyName) || propertyName.Trim().Length == 0)
            {
                return source;
            }

            ParameterExpression parameter = Expression.Parameter(source.ElementType, String.Empty);
            MemberExpression property = Expression.Property(parameter, propertyName);
            LambdaExpression lambda = Expression.Lambda(property, parameter);

            string methodName = (sort == SortDirectionEnum.Ascending) ? "OrderBy" : "OrderByDescending";

            Expression methodCallExpression = Expression.Call(typeof(Queryable), methodName,
                                                new Type[] { source.ElementType, property.Type },
                                                source.Expression, Expression.Quote(lambda));

            return source.Provider.CreateQuery<T>(methodCallExpression);

        }

    }

    /// <summary>
    /// 指定对项列表进行排序的方向。
    /// </summary>
    public enum SortDirectionEnum
    {
        /// <summary>
        /// 从小到大排序。例如，从 A 到 Z。
        /// </summary>
        Ascending = 0,
        /// <summary>
        /// 从大到小排序。例如，从 Z 到 A。
        /// </summary>
        Descending = 1,
    }
}
